Internal combustion engine with exhaust with gas recirculation

ABSTRACT

Supercharged internal combustion engine with exhaust recirculation, in which the exhaust manifold of the engine communicates, via non-return valves and an exhaust conduit, with the inlet manifold of the engine. The non-return valves are arranged to only open when the exhaust pressure in the exhaust manifold is higher than the charged air pressure.

BACKGROUND OF THE INVENTION

The present invention relates to an internal combustion engine,comprising an inlet manifold and an exhaust manifold, respectively,opening into inlet ducts and exhaust ducts, respectively, to the enginecylinders, a charging unit, the pressure side of which is connected toan inlet air conduit opening into the inlet manifold; and a conduit forrecirculation of exhaust from the exhaust side of the engine to itsinlet side.

In supercharged internal combustion engines, e.g. turbo engines, thecharged pressure of the intake air in the intake manifold is oftenhigher than the mean pressure of the exhaust in the exhaust manifold,which means that conventional shutter and valve devices used in suctionengines cannot be used in supercharged engines to transfer exhaust tothe pressure side of the compressor. It is known to achieve this to usesome type of pressure increaser on the exhaust side, e.g. constrictionin the form of a turbo unit with variable geometry, or some form of pumpdevice.

If the principle of pressure increase is used, this means that theengine will work against a pressure with its entire exhaust flow toreturn only a fraction of the flow, approximately 10%, to the inletside, which results in an undesirable loss of efficiency. The principlewith the pump, in addition to the extra cost and complexity, involves aparasitic loss corresponding to the rise in pressure of about 10% of theexhaust flow divided by the efficiency of the pump, i.e. a total ofapproximately 20% of the exhaust flow times the rise in pressure.

SUMMARY OF THE INVENTION

The purpose of the present invention is to achieve an internalcombustion engine of the type described by way of introduction, in whichexhaust can be returned to the inlet side without any loss of efficiencyand with much simpler and less expensive means than a pump device.

This is achieved according to the invention by virtue of the fact thatthe recirculation conduit communicates with valve means and that valvecontrol means are arranged, during such operating conditions where theexhaust is to be recirculated, to only permit the valve means to openwhen the exhaust pressure in the manifold is higher than the airpressure on the pressure side of the charging unit.

The invention is based on the insight that the pressure during thepressure pulsations in the exhaust manifold has pressure peaks, whichexceed the charge pressure in the inlet manifold, and use valve meanswhich open at these pressure peaks but are kept closed therebetween toprevent inlet air from flowing to the exhaust side.

In its simplest form, the valve and control means can be non-returnvalves.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail below with reference toexamples shown in the accompanying drawings, where

FIG. 1 shows schematically a first embodiment of an internal combustionengine with valve and control means according to the invention,

FIG. 2 shows a diagram illustrating exhaust and charge pressure as wellas mass flow of returned exhaust,

FIG. 3 shows a section through a portion of an exhaust manifold with avalve means, and

FIG. 4 shows a view corresponding to FIG. 1 of a second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIGS. 1 and 4, 1 designates a six-cylinder diesel engine with anexhaust manifold 2 and an inlet manifold 3. The exhaust manifold isdivided into two branch portions 2 a and 2 b, each with three branches,which communicate with the exhaust ducts of the engine. The branchportions 2 a,2 b open into the inlet 4 of an exhaust turbine 5, to whicha compressor 6 is drivably coupled. The compressor 6 has an inlet 7 forintake air and an outlet 8 coupled to an inlet air conduit 9, which viaa charged air cooler 10 leads the inlet air to the inlet manifold 3. Theexhaust turbine 5 is joined via an exhaust pressure regulator 11 to anexhaust pipe 12.

13 generally designates a control unit which is known per se and whichis preferably microcomputer controlling different engine and vehiclefunctions depending on engine data fed into the control unit, such ascharge pressure, rpm and air temperature as well as vehicle data such asABS on/off, vehicle speed, accelerator position etc.

Each branch portion 2 a and 2 b is joined to a short pipe 15 a, 15 b,which communicates with the inlet to a non-return valve 16 a, 16 b (FIG.1), the outlet of which is joined to conduits 17 a,17 b, which cometogether and open into a cooler 18, from which a conduit 19 leads to aninlet 20 to the inlet manifold 3 of the engine. In the conduit 19 thereis arranged a regulator valve 21 controlled by a control unit 13. Theregulator valve 21 regulates the flow from the cooler 18 to the inletmanifold 3.

When the operating stage of the engine is such that exhaust can berecirculated to the inlet manifold, the control unit 13 sends signals tothe regulator valve 21 to open the communication between the cooler 18and the inlet manifold 3. As soon as the pressure in the exhaustmanifold 2 of the exhaust pulse exceeds the charged air pressure, i.e.the pressure in the conduit 17 a,17 b, the non-return valve 16 a, 16 bopen and exhaust can flow to the inlet side of the engine. In theexample shown in FIG. 1 with one non-return valve 16 a,16 b for eachgroup of three cylinders, the non-return valves open three times duringtwo rotations of the crankshaft, as illustrated in the diagram in FIG.2, where the curve A represents the exhaust pressure in each branchportion 2 a,2 b; the curve B represents the charged air pressure in theinlet manifold 3 and the curve C represents the massflow of returnedexhaust.

FIG. 3 shows a non-return valve 16 a on a larger scale and arranged sothat its valve disc 31 in the closed position of the valve seals againstthe edge of an inlet 32 which is formed by an opening directly into themanifold wall. The manifold disc 31 is joined to a valve spindle 33,which in turn is loaded by a spring 34, which biases the disc 31 towardsits closed position. By mounting the valve at the shortest possibledistance from the cylinders of the engine, the minimum possible dampingof the exhaust pulses is obtained. In order to protect the valves fromthe high temperature of the exhaust manifold, they are provided withcooling fins 35. The valve 16 a has a pipe stub 36 to which a conduit 17a is to be connected.

The arrangement in FIG. 4 differs from that shown in FIG. 1 in that thenon-return valve 16 a, 16 b are replaced by a pair ofelectromagnetically operated valves 40 a,40 b, which are controlled, viaan amplifier 41, by the control unit 13. The valves and their closingwill be somewhat more complicated than when using the non-return valves16 a,16 b, controlled by the pressure difference between the chargepressure and the exhaust pressure, but on the other hand, thecontrolling can be made more exact. FIG. 4 shows as well an extraregulator valve 42, by means of which the amount of recirculated exhaustis controlled, if the valves 40 a,40 b are of the type which can onlyswitch between open and closed position. If the valves 40 a,40 b areregulator valves with a variable degree of opening, the regulator valve42 can be eliminated. As an alternative to non-return valves orelectromagnetically controlled valves, valves hydraulically controlledby a cam shaft system can be used.

What is claimed is:
 1. Internal combustion engine, comprising an inletmanifold (3) and an exhaust manifold (2), respectively, opening intoinlet ducts and exhaust ducts, respectively, to the engine cylinders, acharging unit (6), the pressure side (8) of which is connected to aninlet air conduit (9) opening into the inlet manifold; and a conduit (17a, 17 b, 19) for recirculation of exhaust from the exhaust side of theengine to its inlet side, characterized in that the recirculationconduit (17 a, 17 b, 19) communicates with valve means (16 a, b; 40 a,b) which are connected directly to the exhaust manifold and that valvecontrol means (13) are arranged, during such operating conditions wherethe exhaust is to be recirculated, to only Permit the valve means toopen when the exhaust pressure in the manifold (2) is higher than theair pressure on the pressure side of the charging unit (6), andcharacterized in that the exhaust manifold (2) is divided into at leasttwo branch portions (2 a, b) which open into a common exhaust pipe (4),and that the valve means comprise one valve (16 a, b; 40 a, b) in eachbranch portion.
 2. In an internal combustion engine having an inlet sidewith an inlet manifold opening to an inlet duct, an exhaust side with anexhaust manifold opening to an exhaust duct, a charging unit having apressure side that communicates with the inlet duct, and a recirculationconduit that recirculates exhaust from the exhaust side to the inletside, the improvement wherein the recirculation conduit communicateswith a valve that opens directly into the exhaust manifold only when apressure in the exhaust manifold exceeds a pressure in the pressure sideof the charging unit.
 3. Internal combustion engine, comprising an inletmanifold (3) and an exhaust manifold (2), respectively, opening intoinlet ducts and exhaust ducts, respectively, to the engine cylinders, acharging unit (6), the pressure side (8) of which is connected to aninlet air conduit (9) opening into the inlet manifold; and a conduit (17a, 17 b, 19) for recirculation of exhaust from the exhaust side of theengine to its inlet side, characterized in that the recirculationconduit (17 a, 17 b, 19) communicates with valve means (16 a, b; 40 a,b) which are connected directly to the exhaust manifold and that valvecontrol means (13) are arranged, during such operating conditions wherethe exhaust is to be recirculated, to only permit the value means toopen when the exhaust pressure in the manifold (2) is higher than theair pressure on the pressure side of the charging unit (6).
 4. Internalcombustion engine according to claim 3, characterized in that therecirculation conduit (17 a, b, 19) communicates with the inlet side viaa cooler (18).
 5. Internal combustion engine according to claim 4,characterized in that the exhaust manifold (2) is divided into at leasttwo branch portions (2 a, b) which open into a common exhaust pipe (4),and that the valve means comprise one valve (16 a, b; 40 a, b) in eachbranch portion.
 6. Internal combustion engine according to claim 3,characterized in that said valve means are formed of at least onenon-return valve (16 a, 16 b) which is arranged to open for exhaustrecirculation when the exhaust pressure in the manifold (2) is higherthan the inlet air pressure.
 7. Internal combustion engine according toclaim 6, characterized in that the recirculation conduit (17 a, b, 19)communicates with t he inlet side via a cooler (18).
 8. Internalcombustion engine according to claim 6, characterized in that theexhaust manifold (2) is divided into at least two branch portions (2 a,b) which open into a common exhaust pipe (4), and that the valve meanscomprise one valve (16 a, b; 40 a, b) in each branch portion. 9.Internal combustion engine according to claim 3, characterized in thatsaid valve means are formed of at least one solenoid valve (40 a, 40 b),which is controlled by a control unit (13), which is arranged, dependingon engine data fed to the control unit, to open the valve when theexhaust pressure in the manifold (2) is higher than the inlet airpressure.
 10. Internal combustion engine according to claim 9,characterized in that the recirculation conduit (17 a, b, 19)communicates with the inlet side via a cooler (18).
 11. Internalcombustion engine according to claim 9, characterized in that theexhaust manifold (2) is divided into at least two branch portions (2 a,b) which open into a common exhaust pipe (4), and that the valve meanscomprise one valve (16 a, b; 40 a, b) in each branch portion.